An anonymous reader quotes a report from Ars Technica: In decades of research, scientists have found only one medical condition that's clearly and effectively treated with testosterone supplements: pathological hypogonadism -- that's low testosterone levels due to disease of the hypothalamus, pituitary gland, or testes. In a series of placebo-controlled, randomized trials, researchers tracked the effect of testosterone on the cognition, bone health, anemia, and cardiovascular health of 788 men for a year. All the men were aged 65 or older and had low testosterone levels that couldn't be explained by anything other than age. The results, reported Tuesday in JAMA and JAMA Internal Medicine, offer mixed results. Among the 493 in the trial who also had age-related memory declines, testosterone didn't have any effect on memory or cognitive abilities. In the study, 247 got testosterone and 246 got a placebo. But for cardiovascular health, there was an effect -- a bad one. Over the year, plaque buildup in the coronary artery -- which is a risk factor for heart disease -- increased in 73 men on testosterone compared with 65 on placebo. However, other studies have found mixed results on this. Longer, bigger trials will be needed to sort out the risks. In the anemia study, testosterone did seem to improve iron levels in men with mild anemia. The bone health study also showed that testosterone could improve bone density. However, it's unclear if those benefits outweigh the possible cardiovascular risks. And other drugs may be more effective at treating anemia and improving bone mass than testosterone.